Combustion chamber comprising a cooling unit and method for producing said combustion chamber

ABSTRACT

The invention relates to a combustion chamber ( 1 ) for a rocket engine, which is used to expel a hot gaseous stream, said combustion chamber ( 1 ) having cooling channels ( 2 ) that are traversed by a coolant. According to the invention, the cooling channels ( 2 ) have a substantially right-angular cross-section and at least some of said channels ( 2 ) comprise depressions ( 6 ), which prevent the stratification of the coolant in the channels ( 2 ). The depressions are formed by the drilling of bores in the combustion chamber wall prior to the production of the cooling channels.

The present invention relates to a combustion chamber for a rocketengine, which is used to expel a hot gas stream, said combustion chamberhaving cooling channels through which a cooling medium flows. Theinvention also relates to a method for producing such a combustionchamber.

The cooling channels that are adjacent to a combustion chamber wallnormally have the objective of keeping the combustion chamber wall socool relative to the hot combustion gases that a sufficiently longservice life of the combustion chamber is ensured. Various solutions areknown from the state of the art for achieving this objective.

German patent application DE 100 54 333 A1 discloses a combustionchamber with a cooling unit as well as with an inner combustion chamberwall adjacent to the interior of the combustion chamber for aregeneratively cooled engine. The inner combustion chamber wall hasdepressions that are configured in such a way that a stable gas streamformed in the area of the inner combustion chamber wall during operationof the combustion chamber becomes destabilized in terms of its flow inthe area of the depressions. This approach is based on the considerationthat the gas stream in the combustion chamber forms a boundary layer inthe area of the combustion chamber wall in the normal case of a smoothcombustion chamber wall, said boundary layer having a certain thermalinsulating effect against the heat input into the combustion chamberwall resulting from the hot gas stream. With that arrangement, anendeavor is made to disrupt the formation of this thermally insulatingboundary layer so as to increase the heat input into the combustionchamber wall and thus into the cooling unit. However, from thestandpoint of manufacturing, creating depressions inside the combustionchamber is technically difficult and expensive.

Furthermore, German patent application DE 101 56 124 A1 discloses arocket engine with a combustion chamber and an expanding nozzle, saidcombustion chamber and/or said expanding nozzle having cooling channelsfor cooling with a liquid. In order to reduce temperature layering(stratification) in the cooling medium, it is provided that at leastsome of the cooling channels have a meander-like geometry, at least insections. As a result of a curvature of the cooling channel, centrifugalforces and Coriolis forces are induced by the resultant flow deflectionas a function of the local curvature radius, said forces manifestingthemselves in the formation of a vortex pair situated in the flow crosssection. This vortex pair ensures a convective flow exchange within thecross section, as a result of which stratification is reduced. However,the production of meander-like cooling channels calls for additionaleffort and raises the costs.

Finally, world patent application WO 02/055864 A1 describes providingthe cooling channels with a surface that guides the cooling medium. Theguide surface imparts the coolant with a rotation when it flows throughthe cooling channel so that a stratification is prevented. In order tocreate the guide surface, it is provided that a metal film is shapedinto the desired form with the guide surface and this intermediateproduct is configured as cooling channels and applied onto a combustionchamber wall. Here, the guide surface is formed by protruding ribs thatare at an angle relative to the axis of the cooling channel. Instead ofribs, it is also proposed that the surface be provided with notches orgrooves. These, too, extend at an angle relative to the axis of thecooling channel in order to impart the desired rotation to the coolingmedium.

Hence, in order to attain an improved heat transfer from the combustionchamber into the cooling medium of a cooling unit, design measures areimplemented in an attempt to prevent temperature layering in the area ofthe combustion chamber wall—either in the combustion chamber itself orin the cooling unit. However, the measures proposed in the state of theart have drawbacks in terms of their handling and production.

Consequently, it is the objective of the present invention to provide acombustion chamber for a rocket engine as well as a method for itsproduction that, in a simple manner, allows a greater heat transfer intoa cooling unit.

This objective is achieved with a combustion chamber having the featuresof claim 1 and with a method having the features of claim 9.Advantageous embodiments can be gleaned from the respective subordinateclaims.

In this context, a combustion chamber for a rocket engine is providedwhich is used to expel a hot gas stream, said combustion chamber havingcooling channels through which a cooling medium flows. According to theinvention, the cooling channels have an essentially rectangular crosssection, at least some of the cooling channels having depressions—whichare preferably arranged on the web walls—by means of which astratification of the cooling medium in the cooling channels isprevented. The fact that the depressions are arranged transverse to theflow direction of the cooling medium results in a reliabledestabilization of the temperature layering.

The provision of cooling channels having an essentially rectangularcross section allows an especially simple production since they can becreated in a combustion chamber wall from the outside of the combustionchamber. The cooling channels can be created, for example, by means of amilling tool, thus eliminating the need for arduous bending or shapingprocedures. In the most favorable case, the width of a cooling channelmatches the width of a milling tool so that the final shape of thecooling channels can be attained with one single machining step. Thecreation of the depressions in at least some of the cooling channels islikewise particularly simple since all of the work can be carried out inthe same machining station in one and the same clamping step.

According to a preferred method, prior to the formation of the coolingchannels in the combustion chamber wall, the depressions can be createdin the area of the longitudinal axis in the form of bores or milledrecesses along said longitudinal axis of the cooling channels. The boresor milled recesses in the area of the longitudinal axis are preferablycreated prior to the formation of the actual cooling channels.

The method according to the invention stands out vis-à-vis thetechniques known from the state of the art in that the obstaclesprovided in the area of a cooling channel are not made after theproduction of the cooling channel but rather already before itsproduction. This translates into major technical advantages from thestandpoint of manufacturing since a combustion chamber according to theinvention can be produced with just a few tools within a short period oftime.

In one embodiment, the depressions are advantageously formedsymmetrically relative to the longitudinal axis in the opposite webwalls. This means that the drilling axis of a drill is positioned on thelongitudinal axis of the cooling channel during the drilling. Thediameter of the drill is selected so as to be larger than the width ofthe cooling channel. Hence, with just one bore, depressions can becreated relative to the longitudinal axis on each of the opposite webwalls. This accounts for an especially fast production.

In another embodiment, the depressions are arranged offset relative tothe longitudinal axis on the opposite web walls. In this variant, thedrilling axis of a drill is positioned laterally offset by an offsetdistance relative to the longitudinal axis of the cooling channel. If,at the same time, the radius of the drill is selected so as to besmaller than the distance of a web wall to the longitudinal axis plusthe offset distance, this then allows an arrangement in which thecooling channel has a depression on one web wall whereas, symmetricallyrelative to the longitudinal axis, it does not have a depression on theopposite web wall. Thus, for instance, it is possible to first createseveral depressions on one web wall in a lengthwise section of thecooling channel and then to create depressions on the opposite web wallin a subsequent section.

Moreover, it is advantageous for the cross section of the depressions tobe configured in the shape of a circle segment, the radius of saidcircle segment being greater than or equal to the depth of thedepressions. In this manner, the groove effect of the depressions isdiminished, which translates into an increase in the service life of thecombustion chamber. In this embodiment, the circle segment can never belarger than a semicircle. A cross section in the form of a circlesegment can easily be created with a drill; a cross section in the formof an ellipsoidal segment would call for a milling procedure.

By varying the density of the depressions—that is to say, especially thenumber of depressions per length section—the obstacle effect of thedepressions on the boundary layer can be varied locally and thus thelocal heat transfer for each area of the combustion chamber wall can beadapted to the conditions and requirements in question. Thus, it ispreferable for the cooling channels to have sections with a differingnumber of depressions. In particular, a combustion chamber can beconsidered that has an injection head that is situated at a first endand a combustion chamber neck that is situated at the end opposite fromthe first end and that serves as an outlet opening for the gas stream.With such combustion chambers, particularly high heat flow values occurin the area of the combustion chamber neck. In order to lower the walltemperatures, a higher number of depressions can be provided in the areaupstream from the combustion chamber neck. This makes it possible toprevent a stratification of the coolant before it reaches the nozzleneck. On the other hand, a combustion chamber as described above has arelatively low heat flow in the area of the injection head since the gasstream has a lower speed and temperature in this area than furtherdownstream. If a lower number of depressions is provided in this area ofthe combustion chamber wall, then the heat transfer can be adjusted sothat the local wall temperature at this place can be adapted to thelocal temperatures in areas of the combustion chamber wall that arelocated further downstream. In this manner, a more uniform walltemperature is achieved over the entire length of the combustionchamber. The increase in the number of depressions in individual areasof the combustion chamber wall, i.e. in the appertaining coolingchannels, can be the same or different.

Here, it is also easily possible for the depressions to have different[sic] along the longitudinal axis of a given cooling channel. Therefore,the circle segments formed by a bore can have different radii on the onehand and can project to different depths into a given web wall on theother hand.

The depth of the bore or milled recess in the radial direction ispreferably selected so as to be smaller than or equal to the height ofthe web walls of the cooling channel. It is easily conceivable for thedepth of a given bore or milled recess to be selected so as to bedifferent.

The invention, its advantages and additional benefits are explained ingreater depth on the basis of the following figures. The following isshown:

FIG. 1 a cross section of a combustion chamber for a rocket engine,

FIG. 2 a section through a partial area of a combustion chamber showingthe arrangement of the depressions relative to the cooling channels and

FIGS. 3 to 5 various embodiments showing the arrangement of thedepressions along a cooling channel, along the line A-A of FIG. 2.

FIG. 1 shows a combustion chamber 1 in a cross sectional depiction. Acombustion chamber wall 3 is provided with a cooling unit in the form ofcooling channels 2 running axially next to each other and each having arectangular cross section. The combustion chamber wall 3 has an innerlayer 4 and an outer layer 5. The cooling channels 2 are created in thecombustion chamber wall 3 from the outside, for example, by means ofmilling. After the cooling channels 2 have been cast with wax, the outerlayer 5 of the combustion chamber wall is formed by a galvanic layer.Subsequently the wax is removed again. The width of a cooling channelis, for example, between 0.7 mm and 1.3 mm.

In order to prevent temperature layering of the cooling medium that hasbeen introduced into the cooling channels, according to the invention,obstacles in the form of depressions are provided in the web walls ofthe cooling channels. As can be seen more clearly from the crosssectional representation of FIG. 2, the depressions are only created inthe area of certain web walls 10. Of course, it would certainly also beeasily possible to provide obstacles on the bottom of a given coolingchannel 2, but this could give rise to service life problems for thecombustion chamber due to premature cracking. Therefore, an arrangementis preferred in which obstacles are only created in the web walls ofcertain cooling channels 2 whereas the bottom 11 remains smooth.

In FIG. 2, the radial depth t_(v) of the depression matches, forinstance, the depth t of the cooling channel. It would, of course, alsobe conceivable to configure the depth t_(v) of the bore so that it issmaller than the depth t of the cooling channel.

The invention is elucidated more clearly in FIGS. 3 to 5, which show atop view of a given cooling channel along the line A-A of FIG. 2 as wellas the depressions created in said cooling channel. The depressions 6,which are located in the web walls 10 and which each have the crosssectional shape of a circle segment, are created in the combustionchamber wall 3 by a bore at the appropriate places in the coolingchannel. Each cooling channel 2 has a longitudinal axis 7 that runsthrough the cooling channel essentially symmetrically relative to theweb walls 10. The flow direction of the cooling medium flowing throughthe cooling channel 2 is indicated by the arrow having the referencenumeral 9.

In the embodiment according to FIG. 3, the bore has a diameter 2 r, saiddiameter being larger than the width b of the cooling channel 2. Twobores 6 are spaced at a distance a from each other. The distance a doesnot have to be uniform along the longitudinal axis 7. On the contrary,it is advantageous to reduce the distance a in areas with a high heatflow such as, for example, the combustion chamber neck, and to enlargethe distance a in areas where the heat flow is less such as, forexample, in the area of the injection head.

The axial depth d_(v) of a given depression is identical in each of thecircle segments shown in FIG. 3. The depth d_(v) of the depression,however, can vary along the longitudinal axis 7. However, in order tokeep the groove effect of the depressions from becoming too large, thecircle segment of a depression should not exceed a semicircle. The depthd_(v) has to be chosen as a function of the selected cooling medium andof the flow velocity. Axial depths in the range from 0.1 mm to 0.2 mmhave proven to be favorable in order to improve the heat transfer by upto 50%.

Only two bores are needed in order to create the four circle segments,that is to say, the four depressions, in the web walls 10 of the coolingchannel of FIG. 3. In contrast, a total of four bores have to be made inthe embodiment of FIG. 4. Whereas the drilling axis 8 of a given bore issituated on the longitudinal axis 7 in the example of FIG. 3, eachdrilling axis 8 in FIG. 4 is arranged offset by an offset distance drelative to the longitudinal axis 7. The radii of these bores aresmaller than the previous embodiment, resulting in a greater grooveeffect. As far as the depth d_(v) of the depression is concerned, likein the abovementioned embodiment, it is sufficient if it is in the rangefrom 0.1 mm to 0.2 mm.

Whereas the depressions are arranged symmetrically relative to thelongitudinal axis 7 in the two described embodiments, the depiction inFIG. 5 shows that the depressions can also be arranged offset relativeto the longitudinal axis. Whereas the bores made in the upper web wall10 are at a distance a₁ from each other, the bores 6 associated with thelower web wall 10 are at a distance a₂. The distances a₁ and a₂ can bebut do not have to be the same. For this embodiment, as well, it ischaracteristic that the bore axes 8 are at a distance from thelongitudinal axis 7. The radius of each bore has to be dimensioned insuch a way that it is less than the distance between the longitudinalaxis 7 and a web wall plus the offset distance d, which is formed by thedistance between the bore axis 8 and the longitudinal axis 7.

An especially simple production of the combustion chamber according tothe invention is possible since the bores 6 are created before theactual production of the cooling channels of the combustion chamberwall. The production only calls for the provision of drilling andmilling tools. Since no sheet metal has to be bent, the cooling channelscan have a smaller width and smaller distance from each other, as aresult of which the surface available for heat transfer is increased.

The distance a, a₁ and a₂ of the depressions relative to each other canbe adapted to the local requirements made of the strength of the heatinput into the combustion chamber wall, that is to say, the localdensity of the depressions can be adjusted over the distance a, a₁ anda₂. In the example according to FIG. 3, the distance is about 2 mm to 5mm, in other words, about ten to fifty times the depth d_(v). Thedensity can be increased or decreased as needed, between completelysmooth areas up to several dozen depressions per centimeter. Asexplained above, it can prove to be advantageous to provide a lowernumber of depressions locally in the area near the injection head aswell as in the area upstream from the combustion chamber neck or else toprovide depressions exclusively in these sections and otherwise toconfigure the cooling channels so that they are smooth.

List of Reference Numerals

-   1 combustion chamber-   2 cooling channel-   3 wall-   4 inner layer-   5 second/outer layer-   6 depression-   7 longitudinal axis-   8 bore axis/mid-point-   9 flow direction-   10 web wall-   11 bottom-   12 injection head-   13 combustion chamber neck-   14 bore axis-   b width of the cooling channel-   t depth of the cooling channel-   r radius of the bore-   a distance between two bores-   a₁, a₂ distance between two bores-   d depth of the depression-   t_(v) depth of the bore-   d offset distance

1-18. (canceled)
 19. A combustion chamber for expelling a hot gas streamfrom a rocket engine, the combustion chamber comprising: a combustionchamber wall; and a plurality of cooling channels arranged inside thecombustion chamber wall and configured to receive a flow of a coolingmedium, each cooling channel defining a longitudinal axis, a depthdirection, and a substantially rectangular cross section, wherein atleast one cooling channel includes a plurality of depressions configuredto prevent a stratification of the cooling medium in the at least onecooling channel, wherein the plurality of depressions are arrangedtransverse to a direction of the flow direction and transverse to thelongitudinal axis in the depth direction.
 20. The combustion chamber asrecited in claim 19, wherein the combustion chamber wall has a firstlayer and a second layer.
 21. The combustion chamber as recited in claim20, wherein the first layer is an inner layer facing an inside of thecombustion chamber and the second layer is an outer layer, and whereinthe cooling channels are arranged in a side of the inner layer facingthe outer layer.
 22. The combustion chamber as recited in claim 21,wherein the depressions extend from the side of the inner layer facingthe outer layer into the inner layer.
 23. The combustion chamber asrecited in claim 19, wherein the at least one cooling channel includesweb walls and wherein the depressions are provided in the web walls. 24.The combustion chamber as recited in claim 23, wherein the depressionsare formed symmetrically relative to the longitudinal axis in oppositeweb walls.
 25. The combustion chamber as recited in claim 23, whereinthe depressions are formed offset with respect to each other in thedirection of the longitudinal axis in the opposite web walls.
 26. Thecombustion chamber as recited in claim 19, wherein each depression has adepression depth and a cross section configured as a circle segmenthaving a radius greater than or equal to the depression depth.
 27. Thecombustion chamber as recited in claim 22, wherein the at least onecooling channel has web walls extending from the first layer to thesecond layer, a maximum depression depth of the depressionscorresponding a web height of the web walls determined by a channeldepth of the at least one cooling channel.
 28. The combustion chamber asrecited in claim 19, wherein the at least one cooling channel includes,along the longitudinal axis, a first area with a first densitydistribution of cooling channels and a second area with a second densitydistribution of cooling channels.
 29. The combustion chamber as recitedin claim 19, further comprising an injection head disposed at a firstend and a combustion chamber neck disposed a second end opposite thefirst end, the combustion chamber neck serving as an outlet opening forthe gas stream, and wherein a lower number of depressions is providedupstream in an area corresponding to the combustion chamber neck.
 30. Amethod for producing a combustion chamber, the method comprising:providing a combustion chamber wall; and forming a plurality of milledrecesses in the combustion chamber wall, along a longitudinal axis andin an area of the longitudinal axis transverse to the longitudinal axis;forming a cooling channel having a substantially rectangular crosssection and opposite web walls inside the combustion chamber wall alongthe longitudinal axis and configured to receive a flow a cooling mediumalong the longitudinal axis, wherein the recesses form depressions inthe web walls walls.
 31. The method as recited in claim 30, wherein themilled recesses are bores.
 32. The method as recited in claim 30,wherein the forming of the milled recesses is performed prior to theforming of the cooling channel, the cooling channel intersecting themilled recesses.
 33. The method as recited in claim 30, wherein theproviding of the combustion chamber wall includes providing a firstcombustion chamber wall layer and subsequently forming a secondcombustion chamber wall layer, and wherein the forming of the milledrecesses and the cooling channel is performed in the first combustionchamber wall layer.
 34. The method as recited in claim 30, wherein theforming of the cooling channels is preformed using a milling tool alongthe longitudinal axis, wherein opposite web walls are formedequidistantly from the longitudinal axis.
 35. The method as recited inclaim 34, wherein the forming of the milled recesses is performed usinga milling tool having a drilling axis positioned on the longitudinalaxis during the forming of the milled recesses.
 36. The method asrecited in claim 35, wherein a diameter of the milling tool is selectedto be larger than a width of the cooling channel.
 37. The method asrecited in claim 36, wherein the milling tool is a drill.
 38. The methodas recited in claim 34, wherein the forming of the milled recesses isperformed using a milling tool having a drilling axis positionedlaterally offset by an offset distance relative to the longitudinal axisduring the forming of the milled recesses.
 39. The method as recited inclaim 38, wherein a radius of the milling tool is selected be smallerthan a distance of the web walls to the longitudinal axis plus theoffset distance.
 40. The method as recited in claim 38, wherein theforming of the milled recesses includes forming a first number of milledrecesses on a first side of the longitudinal axis and forming a secondnumber of milled recesses on a second side of the longitudinal axis. 41.The method as recited in claim 30, wherein the forming of the milledrecesses is performed using different milling tool diameters.
 42. Themethod as recited in claim 30, wherein a recess depth is selected to beless than or equal to a height of the web walls determined by a depth ofthe cooling channel.
 43. The method as recited in claim 30, wherein theforming of the milled recesses includes forming a first number of milledrecesses per unit length in a first channel area and forming a secondnumber of milled recesses per unit length in a second channel areaupstream from the first channel area, wherein the second number of boresper unit of length is greater than the first number of milled recessesper unit length.